Method of stabilizing platinum group metal reforming catalyst



United States Patent OfiFiee 3,347,782 METHOD OF STABILIZING PLATINUMGROUP METAL REFORMING CATALYST Leon M. Capsuto, Woodbury Heights, andFrancis E.

Davis, in, Westville, N.J., assignors to Mobil Oil Corporation, acorporation of New York No Drawing. Filed Sept. 9, 1963, Ser. No.307,297 1 Claim. (Cl. 208-138) 3,347,782 Patented Oct. 17, 1967 actionconditions such that the partial pressure of water vapor in the efiiuentof the reaction zone, i.e., the eflluent of the last reactor in amulti-reactor unit is less than 0.4 millimeter of mercury and preferablyless than 0.2 millimeter of mercury.

As disclosed in the application Serial Number 45,827 the cycle life of aplatinum alumina reforming catalyst is substantially improved byreforming under desiccated conditions. However, although by operatingunder conditions of desiccated reforming the on-stream time issubstantially increased, nevertheless the selectivity of theplatinum-group metal reforming catalyst having an alumina base, i.e., arefractory oxide base having acid sites, de creases with time as clearlyshown by the data presented in Table I. It Will be observed that thisloss in selectivity occurs under desiccated conditions at low reformingpressure, e.g., 200 p.s.i.g. and at high reforming pressure, e.g. 500p.s.i.g. and with both light and heavy naphthas.

B. (la-290 F. kuwait naphtha, 103.5 CB+(R+3) O.N., 200 p.s.i.g.

On-stream time, days 5 13 85 (3 Reformate, Percent of chg 62. 5 61. 5 60H2 production, s.c.f.b 920 850 790 750 Loss of Selectivity:

06+ Reformate, Percent of chg Base 2. 5 3. 5 5.0 Hz production, s.c.f.bBase 170 O. ISO-365 F. kuwait na htha, 104.5 C+(R+3) 0.N., 500 p.s.i.g.

On-stream time, days 5 10 60 105 0 Reformate, Percent of chg 59. 2 58. 857. 0 55. 5 H2 production, s.c.f.b 580 555 435 330 Loss of Selectivity:

05+ Rcformate, Percent of chg Base 0.4 2. 2 3. 7 H production, s.e.f.bBase 25 250 D. C@-290 F. Aramco, 103.5 Cs+(R+3) ON, 200 p.s.i.g.

On-stream time, days 5 13 25 06+ Reformate, Percent of chg 65 62. 5 61.5Loss of selectivity: 0 yield percent of chg 2. 5 3. 5

E. C 290 F. Aramco, 104.5 Ce+(R+3) O.N., 500 p.s.i.g.

On-stream time, days 5 10 60 105 0 Reformate, Percent of clig 59. 2 58.8 57.0 55.5 Loss of selectivity: 08+ yield, percent of chg 0. 4 2. 2 3.7

it is general experience that the selectivity of platinumgroup reformingcatalysts having a support comprising refractory oxide having acid sitesdecreases with the time on-stream.

As defined in the copending application for United States Letters PatentSerial Number 45,827 filed July 28, 1960 now abandoned in the name ofLeon M. Capsuto desiccated reforming is defined as reforming under re-65 While two to five 70 advantageous compared 3 No. 2,952,611 issued toM. R. Haxton et al. on September 13, 1960. In reforming at highpressure, e.g., 500 p.s.i.g., the cycle life improvement obtained withdesiccated reforming permits operation at lower recycle ratios with animportant savings in investment and operating costs.

Thus, the operator of a reforming unit employing platinum-group metalreforming catalyst having a supcaught between the horns of a dilemma.One horn is the reduced capital and operating costs and the other hornis the loss of selectivity when the catalyst has been onstream more thanthree days as taught by Haxton et al. (supra).

It is customary to distinguish between the activity of a catalyst andthe selectivity of a catalyst. The most readily determined measure ofthe activity of a platinum-group metal catalyst comprising platinum onrefractory oxide support having acid sites is the reforming temperaturerejuired at the vapor inlet of the reaction zone, i.e., the vapor inletof each of a plurality of reactors in a multireactor reaction zone, toproduce C and heavier reformate having a selected predetermined octanerating (Research-+3 cc. TEL) appreciably greater than the octane ratingof the charge naphtha at a selected liquid hourly space velocity andunder a selected total reactor pressure.

On the other hand, the selectivity of a reforming catalyst of the classdefined hereinbefore is most readily determined by the volume of C andheavier reformate and the volume of hydrogen produced at any selectedpredetermined octane rating of the reformate at the selected pressure atany selected time in the on-stream cycle. Thus, for example, theactivity may be substantially constant for a period of time but theselectivity may decrease.

It has now been discovered that the selectivity of a platinum-groupmetal reforming catalyst having a refractory oxide support having acidsites can be maintained substantially constant for more than ninety daysas the data presented in Table II establishes.

presence of platinum-group metal reforming catalyst comprising 0.6percent by weight of platinum and 0.7 percent by weight of chlorine onalumina support is achieved by adding to the feed a nitrogen compoundwhich yields ammonia under the desiccated reforming conditions andpreferably a nitrogen compound yielding ammonia but no water under thedesiccated" reforming conditions. Exemplary of nitrogen compoundsyielding ammonia but no water under desiccated reforming conditions arethe heterocyclic nitrogen compounds pyridine and pyrrole. Simplest ofthe nitrogen compounds yielding no water under the conditions ofdesiccated reforming is gaseous ammonia, NH Exemplary of compoundsyielding ammonia and water under the conditions of desiccated reformingis hydroxylamine (NH OH) To stabilize the selectivity of platinum-groupmetal reforming catalysts having refractory oxide bases containing acidsites at least two to four and preferably about ten to fifteen parts permillion (p.p.m.) by weight of nitrogen as a compound-yielding ammonia(NH under the conditions of desiccated reforming are added to the feed.As the data in Table III establish, 2.6 ppm. of nitrogen fails tocompletely stabilize the selectivity of the platinumgroup metalreforming catalyst of the aforedescribed class while 7 p.p.m. ofnitrogen appears to maintain the catalyst at the higher level ofselectivity.

After start-up about five days are required for the unit to line out andcome to equilibrium. Accordingly, the yield of C and heavier reformaterecovered during the fifth day is considered the base yield measuringthe selectivity of the catalyst. It will be observed that in ten tofifteen days the catalyst had lost selectivity as measured by a loss of2 percent in the yield of C and heavier reformate. Upon the addition of6 ppm. by weight of nitrogen as pyridine the yield of C and heavierreformate and the amount of hydrogen produced returned to the base yieldas TABLE II 0 -250 F. kuwait naphtha, 103.5 C54, (Bi-3) O .N., 200p.s.i.g. On-Stream Time, Days 5 30 110 136 (35+ Reformate, Percent ofcharge 58. 5 59. 0 58. 5 57. 5 58.8 57. 8 56. 5 56. 5 Hydrogen producedper barrel of feed..- 810 850 820 710 830 707 730 740 TABLE III Feed: 01to 250 F. EBP Fraction of Kuwait Naphtha. Catalyst: 0.6 wt. percent Pt.and 0.7 wt. percent Chorine on eta Alumina.

Nitrogen Compound: Pyridine.

Catalyst Age, Days H 5 15 30 40 60 75 1 85 85 Nitrogen in Naphtha,p.p.I11. by w 6. 0 2. 6 6. 9 7. 1 Nil Nil 10. 6 Octane Number (R+3 cc.TEL) of (3 Reformate 103. 5 103. 5 103. 5 103. 5 103. 5 103. 5 103. 5 0.Reierruate, percent by volume of chaige. 58. 5 57. 5 58.8 57. 8 5t. 054. 0 56.0 A percent volume CH Reiormate. 0. 0 1.0 +0. 3 0. 7 t. 5 4. 52. 5 H2 Produced/blah, S.c.f 820 710 830 770 600 600 730 A H:Produced/blah, s.c.f Base 70 +40 +10 100 +20 40 210 210 80 It ismanifest, if for reasons explained hereinafter the yield of C reformateat sixty days on-stream is disregarded, the average yield of C reformateis 58.5%+0.5 and 0.7 percent and the production of hydrogen averaged 816s.c.f. per barrel +34 and 46 s.c.f./b.

The stabilization of the selectivity as measured by the yield of C andheavier reformate (C reformate) when operating under desiccatedreforming conditions in the measured on the thirtieth day. The yield ofC and heavier reformate and the production of hydro-gen were stabilized70 during the period from the thirtieth to the fortieth day while 6p.p.m. of nitrogen as pyridine were being added to the feed. However,when the amount of nitrogen added to the feed was reduced to 2.6 ppm.from 6.0 ppm. of nitrogen, the selectivity of the catalyst declined 75as measured by the yield of C and heavier reformate and the amount ofhydrogen produced on the sixtieth day. The selectivity of the catalystwas restored by increasing the dosage of pyridine from the equivalent of2.6 p.p.m. of nitrogen to 6.9 p.p.m. of nitrogen as measured by theyield of C and heavier reformate and the hydrogen produced on theseventy-fifth day. The selectivity of the catalyst was maintainedthrough the eighty-fifth day by the continued addition of pyridine inamount equivalent to 7.1 p.p.m. (1 p.p.m. of nitrogen is equivalent to5.64 p.p.m. of pyridine). It is now clear why the yield of C and heavierreformate at sixty days on-stream was disregarded when discussing proofof stabilization of selectivity hereinbefore.

The introduction of nitrogen into the reaction zone during reforming isnot novel. This is clear from the fact that US. Patent No. 2,849,377issued to H. B. Ogburn et al. on August 26, 1958, for a method ofobtaining maximum isomer production when catalytically reforming ahydrocarbon fraction boiling within the gasolinekerosine range. Thesepatentees postulate that the temperature for maximum isomer productionat high selectivity is of less severity than is the reaction temperaturefor the maximum production of aromatics. The patentees accordingly teachto increase the reaction temperature for maximum isomer production athigh selectivity in the direction of the severity of the reactiontemperature for producing maximum aromatics and conducting the reformingprocess in the presence of at least one nitrogen compound from the groupconsisting of ammonia and compounds which will yield ammonia withoutdeposition of a solid residue on the catalyst in an amount sufiicient topermit an increase in the reaction temperature applicable to maximumisomer production at the desired selectivity and increasing the reactiontemperature within the range of the reaction temperature for the maximumproduction of aromaticsThe present process difiers from that describedby patentees Ogburn et al. in that 1) the patentees are not concernedwith and do not discuss the moisture content of the reaction zone vaporsas measured at the effiuent of the reaction zone, i.e., in a threereactor unit at the outlet of the third reactor, (2) the patenteesspecifically recommend the use of ammonium hydroxide without anyprovision for removing water to maintain a partial pressure of waterless than 0.4 millimeter in the efiluent of the reaction zone, (3) thepatentees teach to add 0.06 percent by weight of nitrogen as ammoniumhydroxide or six parts per ten thousand parts of feed, (4) the patenteesteach that a maximum temperature of 950 F. is to be employed. Thepresent method of stabilizing the selectivity of platinum-group metalcatalyst having a support of refractory oxide containing acid sitesprovides for employing a nitrogen compound yielding ammonia in the rangeof 2 p.p.m. to 100 p.p.m. and a temperature in the range of about 900 F.to about 1,050" F. while maintaining a partial pressure of water in theefiluent of the reaction zone less than 0.4 millimeter and preferablyless than 0.2 millimeter of mercury.

In US. Patent No. 2,944,090 issued July 5, 1960, to I. A. Guthrie, aprocess for increasing the quantity of ben zene which can be producedfrom C naphthenes when using as a catalyst platinum supported on ahalogen-containing alumina is described. The patented method consists incontacting a saturated fraction comprising methyl cyclopentane in thepresence of added hydrogen and from 3 to about 8.5 parts per million ofammonia based on the hydrocarbons. The patented method difiers from thepresent method in that 1) the patented process is not concerned with thepartial pressure of water vapor in the final efliuent of the reactionzone, i.e., the effiuent of the last reactor of a plurality of reactors,(2) the patentee finds that the addition of ammonia in the range of 2.5to 7 p.p.m. of nitrogen increases the conversion of C naphthenes tobenzene. In contrast it has been found that in stabilization of theselectivity of a reforming catalyst of the herein defined class theincrease of the C yield appears to be evenly distributed among Cparafiins, toluene, and C aromatics with the benzene yield remainingconstant.

In U.'S. Patent No. 2,956,945 issued October 18, 1960, and in thecorresponding British Patent No. 888,832 published February 7, 1962, R.Fleming et al., teach that the addition of ammonia or a nitrogencompound yielding ammonia in the range of 2 to parts per million or1.647 to 82.35 p.p.m. of nitrogen to a gasoline boiling rangehydrocarbon fraction substantially free of naphthenes, i.e., containing10 percent or less by volume of naphthenes, produces a higher octanenumber product at a given yield than is obtainable by a conventionalreforming process. This patented process differs from the present methodof stabilizing the selectivity of a platinumgro-up metal reformingcatalyst of the hereinbefore defined class in that (1) partial pressureof water vapor in the final effluent of the reaction zone to less than0.4 millimeter of mercury, (-2) Fleming et al. limit the naphthenecontent of the feed to 10 percent by volume or less whereas the presentmethod of stabilizing the selectivity of a platinum-group metalreforming catalyst of the hereinbefore defined class is not so limited,(3) Fleming et al. find that when ammonia is added to the feed thereformate is less aromatic than that produced without ammonia whereas inthe present method the increased yield of (3 reformate is evenlydistributed among C parafiins, toluene, and C aromatics with the benzeneyield remaining constant, (4) the patentees teach that for their purposethe ammonia is added just prior to the last catalyst case in amulticase, i.e., multi-reactor unit for if added earlier the ammoniawill have an adverse effect upon the yield-octane relation. In contrast,to stabilize the selectivity of a platinum-group metal reformingcatalyst of the hereinbefore identified class in accordance with thepresent process the nitrogen compound yielding ammonia under desiccatedreforming conditions is mixed with the feed prior to the first case orreactor of a multicase or multi-reactor unit.

Other U.S. patents describing the addition of ammonia or nitrogencompounds yielding ammonia in a reforming reaction are: Nos. 2,758,064;2,872,494; 2,906,699; 2,911,356; 2,925,375; 2,935,464; and 2,980,605.

Accordingly, the present invention provides a method of stabilizing theselectivity of platinum-group metal reforming catalyst having arefractory oxide support containing acid sites when reforming a lightnaphtha fraction comprising naphthenes and paraffins having an initialboiling point of about to about 250 F. at a pressure in the range of 100to 700 p.s.i.g. and preferably at a pressure in the range of 200 to 500p.s.i.g. in the presence of hydrogen at a liquid hourly space velocityin the range of 0.5 2 v./hr./v., at a hydrogen-to-naphtha mol ratio of 3to 20, employing at least one reactor and preferably at least tworeactors all of which are normally on-stream, i.e., there is no swingreactor and all of the catalyst in all of the reactors normally ison-stream, and vapor inlet temperatures dependent upon the activity ofthe catalyst and the target octane rating (Research+3 cc. TEL) of the Cand heavier reformate in the range of 98 to 113 characterized byadmixing with the naphtha feed prior to entry into the reaction zone,i.e., prior to entry into the first reactor of a plurality of reactorseach containing a static bed of platinum-group metal reforming catalystof the class hereinbefore defined, ammonia, or at least one organiccompound containing nitrogen which under reforming conditions yieldsammonia, and preferably an organic nitrogen compound yielding ammoniaand no water, in a concentration of at least 2 p.p.m. of ammonia,preferably 10 to 15 p.p.m. of ammonia and up to 100 p.p.m. of ammonia,and maintaining a partial pressure of water in the final effluent of thereaction zone, e.g., the effluent of the last reactor in a multi-reactorunit, less than 0.4 millimeter and preferably less than 0.2 millimeterof mercury. As the activity of the catalyst decreases with on-streamtime the vapor inlet temperature Fleming et al. do not limit the i 7 ofthe reactor or reactors is raised to not higher than about 1,050 F. Attemperatures above 1,050 P. the advantages accruing from the admixtureof ammonia and the consequent stabilization of the selectivity of thecatalyst diminsh due to the thermal reforming which occurs attemperatures higher than l,050 F.

The present method of stabilizing the selectivity of platinum-groupmetal reforming catalysts is also effective when reforming paraffinicheavy naphthas employing high pressures, e.g., 400 to 700 p.s.i.g. (incontrast to low pressures in the range of 100 to 400 p.s.i.g.) asdescribed hereinafter.

In a multireactor reaction zone the hereinbefore identified class ofplatinum-group metal reforming catalyst is distributed evenly among allof the reactors or cases or is distributed unevenly. That is to say, thefirst reactor can be charged with the amount of catalyst required toproduce a maximum difference between the temperature of the vaporsentering the first reactor or case and the temperature of the vaporsleaving the first reactor or case as described in US. Patent No.2,946,737, and the balance of the catalyst required to provide thepredetermined liquid hourly space velocity charged evenly or otherwiseto the balance of the reactors or cases. On the other hand, the firstreactor can be operated in a manner approaching isothermicity underwhich conditions the amount of catalyst in the first reactor or case isless than 2 tons per 10,000 barrels of naphtha treated per day asdescribed in copending application for United States Letters PatentSerial No. 109,025 filed May 10, 1961, now abandoned, in the name ofGeorge I. Weidenhammer. Thus, while the overall liquid hourly spacevelocity, i.e., the ratio of the barrels of naphtha treated per hour tothe total barrels of catalyst contacted in all of the reactors or casesin the reaction zone is in the range of 0.5 to 2, the liquid hourlyspace velocity in any reactor or case is a multiple of the overallliquid hourly space velocity and can be the same for all reactors orcases or different for each reactor or case or the same for two or morereactors or cases and different for one case.

As described in the copending application for United States LettersPatent Serial No. 45,827 filed July 28, 1960, in the name of Leon M.Capsuto desiccated reforming is reforming in which the partial pressureof water vapor in the efiluent of the reaction zone, i.e., the efiluentof the last reactor of a multi-reactor reforming unit, does not exceed0.4 millimeter of mercury and preferably is in the range of 0.05 to 0.2millimeter of mercury. Furthermore, as stated in application Serial No.45,827 there are three sources of Water, to wit: the charge naphtha, theundried recycle gas, and the moisture of the catalyst. When the chargenaphtha contains 15 ppm. (part per million) by weight of water, thewater in the charge naphtha contributes about 0.08 millimeter of mercurypartial pressure of water vapor at 200 p.s.i.g. This partial pressure ofwater vapor is increased to about 0.5 to 2.0 millimeter of mercurypartial pressure of water vapor at 200 p.s.i.g. by the water vapor inundried recycle gas. The catalyst also contributes to the concentrationof Water vapor in the effluent of the reaction zone until the catalystis in equilibrium with the moisture content of the reaction zone vapors.Consequently, as described in application Serial Number 45,827 it ispreferred to condition particle-form solid platinum-group metalreforming catalyst having a refractory oxide support containing acidsites in the manner described therein. However, the total amount ofwater introduced into the reaction zone from all sources should notexceed 0.4 millimeter and preferably should be in the range of 0.05 to0.2 millimeter of mercury. Consequently, the degree to which themoisture content of any of the three sources of water, i.e., the naphthafeed, the recycle gas, and the catalyst is reduced grossly is dependentupon the moisture content of the other two. Thus, it is relatively easyto dry naphtha to a moisture content of 10 to ppm. by

weight of water in commercial quantities. At a hydrogentonaphtha recycleratio of 7:1 this amount of water Will build-up to produce atequilibrium a partial pressure of water of about 0.5 to 2.0 millimetersof mercury of 200 p.s.i.g. Accordingly, the charge naphtha is dried tocontain less than 10 ppm. by weight of water by contact with anysuitable desiccant such as the crystalline aluminosilicates generallyreferred to as molecular sieves and having pores about 4 to S Angstromsin diameter, silica gel, and the like. The recycle gas is dried to amoisture content not greater than 5 p.p.m. by volume of water. Thecatalyst is dried, while maintaining maximum surface area, to a moisturecontent not more than 1.1 percent greater than the moisture content ofsaid catalyst after ignition for 48 hours at 1250 C. While it ispreferred to dry the catalyst to obtain conditioned catalyst as definedin application Serial Number 45,827 it is recognized that after severaldays on-stream the water on the catalyst equilibrates with the water inthe catalyst environment and the Water content of the recycle gas dropsto a level dependent upon the moisture content of the feed naphtha andthe temperature of the liquid-gas separator in which the separation ofthe recycle gas, i.e., gas comprising hydrogen, and C to C hydrocarbons,from the raw reformate, i.e., comprising C and heavier hydrocarbons ismade. Hence, when willing to accept the loss in yield for five or sixdays at the beginning of an onstream period, and/or a shorter cyclelife, the catalyst need not be conditioned. In other Words, as describedin the co-pending application Serial Number 45,827, one or more of thesources of water, viz: catalyst, recycle gas, and charge naphtha is orare treated to reduce the water content thereof to provide a partialpressure of water in the efiluent of the reaction zone, i.e., theeffluent of the tail reactor or case of a multi-reactor or casereforming unit, not in exces of 0.4 and preferably in the range of 0.05to 0.2 millimeter of mercury at 200 p.s.i.g. As more fully described inco-pending application Serial Number 45,827 and incorporated in thepresent application by reference herein thereto.

In general, the present method of stabilizing the selectivity ofparticle-form solid platinum-group metal reforming catalyst having arefractory oxide support containing acid sites, comprises contactingcharge naphtha containing innocuous concentrations of sulfur, nitrogen,and arsenic, i.e., not more than 20 ppm. of sulfur, not more than 1 ppm.of nitrogen and not more than 1/10 parts of arsenic, i.e., 1 p.p.b. ofarsenic with particleforrn solid platinum-group metal reforming catalystcomprising platinum-group metal on refractory oxide support having acidsites at an overall liquid hourly space velocity in the range of 0.5 to5 or in a single isothermal re actor dependent upon the activity of theaforesaid platinum-group metal reforming catalyst and the target octanerating (Research-H cc. TEL) of the C and heavier reformate underdesiccated reforming conditions such that the partial pressure of watervapor in the effluent of the reforming reaction zone, i.e., in theefliuent of the tail reactor of a multi-reactor reforming unit, does notexceed 0.4 millimeter and preferably is in the range of 0.05 to 0.2millimeter and admixing with the influent of the reforming reactionzone, i.e., the influent of the head reactor of a multirea-ctorreforming reaction zone, a nitrogen-containin-g compound yieldingammonia (NI-I in the reaction zone and preferably a nitrogen-containingcompound yielding ammonia (NH but no water in the reaction zone inamount to provide a concentration of ammonia (NH in the feed in therange of two to one hundred, preferably ten to fifteen p.p.m. of ammonia(NH Maintaining vapor inlet temperature at the vapor inlet of eachreactor in a multi-reactor reaction zone in the range of 900 to 1050 F.dependent upon the liquid hourly space velocity employed and the targetoctane rating (Research+3 cc. TEL) of the C and heavier reformateproduced in the range of 98 to 113, continuing to admixing saidnitrogen-containing compound with said influent of the reaction zone inamount suflicient to maintain the selectivity. Alternatively, largeramounts of nitrogen-containing compound can be admixed at intervals whennecessary to maintain the selectivity. Thereby, onstream periods inexcess of sixty days without substantial loss of selectivity atpressures in the range of atmospheric to 500 p..i.g. are obtained whenproducing C and heavier reformate having an octane rating in the rangeof 98 to 113 (Research-#3 cc. TEL).

Exemplary of the present method of stabilizing the selectivity ofparticle-form solid platinum-group metal reforming catalyst comprisingplatinum-group metal on refractory oxide support having acid sites isthe reforming of the C to 250 F., (EBP) fraction of Mid-Continentnaphtha under desiccated reforming conditions and in the presence ofabout ten to about twenty p.p.m. by weight of ammonia entering thereactor, at a pressure of 200 p.s.i.g., at a hydrogen-to-naphtha recycleratio of 7:1, and at an overall liquid hourly space velocity of 0.8 toproduce C and heavier raw reformate having an octane rating (Resea-rch+3cc. TEL) in the range of 103 to 111.

While it is preferred to employ three adiabatic reactors charged withthe total amount of catalyst required to produce the predeterminedoverall liquid hourly space velocity as few as two adiabatic reactors orfirst isothermal reactor and one or more adiabatic reactors can be used.For the purpose of this illustration a unit comprising a head, anintermediate, and tail adiabatic reactors will be described havingone-third of the total catalyst in each of the three reactors.

The present method of stabilizing the selectivity of the hereinbeforedefined class of platinum-group metal reforming catalysts is applicableto the reforming of naphthas containing naphthenes or substantially freeof naphthenes, i.e., mixture comprising pa-raflins and naphthenescontaining as little as ten percent by volume of naphthenes and as muchas sixty-five percent by volume of naphthenes. However, presently it ispreferred to treat mixtures comprising about to about 45 percent byvolume of naphthenes and the balance predominantly paraifins.

Where anhydrous ammonia is available at an economically attractiveprice, anhydrous ammonia can be used as the nitrogen-containingcompound. Otherwise organic nitrogen-containing compounds such aspyridine, pyrrole, hydrazine, and the like can be used.Nitrogen-containing compounds such as hydroxylamine, alkylanolamines andother nitrogen-containing compounds producing not only ammonia but alsoWater in the presence of hydrogen and the platinum-group metal reformingcatalyst can be used at the expense of impaired catalyst performance andincreased drying facilities for drying the recycle gas and/ or thecharge naphtha to maintain the partial pressure of water vapor in thefinal reaction zone efiluent at a level not in excess of 0.4, preferably0.05 to 0.2 millimeter of mercury.

For ease of control of the amount of ammonia entering the reaction zoneit is preferred to reduce the nitrogen content of the charge naphthawhen necessary to not more than one p.p.m. by weight.

Thus, the C to 250 F. (EBP) fraction of Mid-Continent naphtha having thefollowing composition:

Hydrocarbon class:

Paratfins vol. pct 53 Naphthenes vol. pct 44 Aromatics vol. pct 3 Othersvol. pct nil Nitrogen, p.p.m. less than 1 Sulfur, p.p.rn. less than 10admixed with hydrogen-containing recycle gas to provide a charge mixturecomprising hydrogen and naphtha in a mol ratio in the range of 1 to 10mols of hydrogen per mol of naphtha and preferably in the range of 5 to9 mols of hydrogen per mol of naphtha is heated to a tem-' perature toprovide at the vapor inlet of the head reactor a reforming temperaturein the range of about 900 to about l,050 F. Nitrogen-containing compoundsuch as ammonia, pyridine, pyrrole, hydrazine and, in general, anynitrogen-containing compound yielding ammonia (NH in the presence ofplatinum-group metal reforming catalyst and hydrogen and preferably notyielding water is admixed with the naphtha and/or the charge mixtureprior to entry of the charge mixture into the re action zone, i.e., thehead reactor in amount to provide a total concentration of ammonia(NH;,) in the charge mixture of at least two and preferably at least tenppm. by weight based on the charge naphtha depending on the severity ofreaction conditions as measured by the octane rating of the C andheavier reformate, catalyst age, charge stock and the like factors.However, concentrations in excess of the equivalent of one hundredp.p.m. by weight of ammonia appear to yield diminishing returns. Thecharge mixture and admixed nitrogen-containing compound flow downwardlythrough the head reactor to the outlet thereof. Since the temperature ofthe efiiuent of an adiabatic head reactor is usually lower than thereforming temperature required by the space velocity and the activity ofthe catalyst to produce reformate of predetermined octane rating, theefliuent of the head reactor, designated head effluent is reheated to atemperature to provide at the vapor inlet of the intermediate reactor(usually an adiabatic reactor) a reforming temperature in the range of930 to 1,050 F. dependent upon space velocity and catalyst activity toproduce reformate of the required octane rating. The reheated headefiluent flows downwardly through the intermediate reactor to the outlet thereof and is reheated to a temperature to provide a reformingtemperature at the vapor inlet of the tail reactor in the range of 930to l,050 F. dependent upon space velocity, catalyst activity, andpredetermined octane rating of the raw reformate, i.e., C and heavierreformate. The reheated intermediate efiluent flows downwardly throughthe tail reactor to the outlet thereof. The final effluent, i.e., theeffluent of the tail reactor, is cooled by indirect heat exchange withthe charge naphtha and finally by indirect heat exchange with water to atemperature at which C and heavier hydrocarbons condense at the existingpressure. Usually, the final efliuent is cooled to a temperature in therange of to F. dependent upon the volume and temperature of the coolingwater. However, the lower the temperature at which the C and heavierhydrocarbons are condensed, the lower the moisture content of theseparated reformer gas, the lower the moisture content of the recyclegas and the less the load on the desiccant used to dry the recycle gasto maintain the partial pressure of water in the final efiiuent nothigher than 0.4 and preferably in the range of 0.05 to 0.2 millimeter ofmercury.

Illustrative of the stabilization of the selectivity of platinum-groupmetal reforming catalyst at 200 p.s.i.g. by admixture ofnitrogen-containing compound yielding ammonia in the presence of saidcatalyst and hydrogen under desiccated reforming conditions are the datapresented in Table IV.

TABLE IV Feed: C to 250 naphthenes) Catalyst: 0.6

on eta alumina support. Reaction Conditions Pressure, p.s.i.g. 200.Liquid Hourly Space Velocity. v./hr./v., 0.8. Hydrogen-toNaphtha Moiratio, 'T/1. Temperature to produce, 105 Cs+(R+3) O.N.

percent by weight of platinum, 0.7 percent by wei F. (EBP) fraction ofMid-Continent Naphtha (44% g-ht of chlorine Days on stream 5 1 10-1619-38 40-54 NHi in naphtha p.p.m. by wt. Nil Nil 10-20 Nil Yields at 105(R-Hi) 0.N. Oat, percent charge 59. 5 56 60 54-55 Hz, S.C.f.lb 1,1301,000 1,150 880 Hz, Purity, M01 percent. 75. 5 71. 5 66 0 's, vol.percent charge. 11. 5 10. 5 11. 5 04's, vol. percent charge 10. 5 l2. 50 l2. 5 C1 to 03, wt. percent charge 13. 5 15. 5 12. 5 16. 5

1 Pyridine added to charge mixture.

' Catalyst thereafter partially coked, accelerated aging,

From these data it is to be observed that deposition of hydrogenproduced and the purity of the recycle gas were coke on the catalystproduces a loss in yield (3.5% yield of (1 130 s.c.f./b. of hydrogen and4 percent in the purity of the hydrogen). The presence of 10 to 20 ppm.of ammonia counteracts the effect of the coke and restores the yields tothe high level obtained with uncoked catalyst. Withdrawing the ammoniaproduces a loss of yields to even lower levels than were obtained afterthe catalyst was coked.

Illustrative of the stabilization of the selectivity of platinum-groupmetal reforming catalyst'at 200 p.s.i.g. by admixture ofnitrogen-containing compound yielding ammonia in the presence of saidcatalyst and hydrogen under desiccated reforming conditions are the dataset forth in Table V.

TABLE V A (Virgin Catalyst) naphthenes) about 2 percent, 140 s.c.f./b.,and 7 percent greater respectively than after 105 days on-stream withoutthe addition of ammonia.

From these data it is manifest that the admixture with the chargemixture of at least six, preferably at least ten,

.p.m. of ammonia by weight based on the charge naphtha stabilizes theselectively of the particle-form solid platinum-group metal reformingcatalyst comprising platinum-group metal on refractory oxide supporthaving acid sites at substantially constant severity as measured by theyield of 0 or 6 reformate and an octane rating (Research-H cc. TEL)higher than the octane rating of the charge naphtha, the standard cubicfeet (s.c.f.) of hydrogen produced per barrel of charge naphtha, and theby weight of Chlorine on eta alumina support.

Days on stream 5 l 15 NHa in Naphtha, ppm. by wt Nil Nil Yields:

05+ Percent charge 61. 5 58. 5 Hi, 5 c 930 850 H2, Purity, M01 Percent71 65 0 's, vol. Percent charge" 9. 5 9. 5 (3 's, vol. Percent charge 9.5 11.0 C1 to C3 wt. Percent charge 14.0 16.0

B (Regencrated Catalyst) Days on stream 5 15 l 75 85 105 138 $11111 innaphtha, ppm. by wt.* Nil Nil 6 7 '1 10 11 B Z 1 Oi Percent charge 5 559. 0 59. 0 58.0 56. 5 56. 0

H, Purity, Mol Percent... 64 67 66 63. 5 59. 5

(3 's, vol. Percent charge..- 9. 5 8.5 9. 0 9.5 9.0 8.0

04's, vol. Percent charge.. 12.0 10.5 11.0 11. 5 11.5 12. 5

C1 to C3 wt. Percent charge 17.0 16.0 16.0 16. 5 17.5 18.0

Pyridine added to charge mixture.

Upon examining the data presented in Table V, Section purity of theproduced hydrogen as measured by the mol A, it will be found that in10.5 days on stream (1) the percent of hydrogen in the reformer gas,i.e., the gas yield on (3 reformate decreased from 61.5 to 54.5perseparated from the reformate at the liquid-gas separator. cent, (2)the yield of hydrogen per barrel decreased from While desiccatedreforming (partial pressure of water 930 to 590 s.c.f./b. and (3) thepurity of the hydrogen less than 0.4 mm. Hg) at low pressures, less than400 dropped 71 to 53 mol percent. On the other hand, the p.s.i.g. withthe addition of at least 2 ppm. of ammonia data in Table V, Section Bshow that the yield of C has been discussed extensively hereinbefore,the addition and heavier reformate was substantially unchanged, theyield of hydrogen per barrel increased and the purity of the hydrogenwas substantially constant with the result that, after 138 dayson-stream with the addition of amof ammonia to the heavy paraflinicnaphthas used as charge stocks in high pressure (400 to 700 p.s.i.g.)reforming provides similar advantages even when the partial pressure ofwater is as high as 5 to 20 mm. Hg.

monia and using a regenerated catalyst, the C ,L yield, the 75 This isestablished by the data presented in Table VI.

TABLE VI Section A Charge Stock: Heavy Kuwait Naphtha BR: 190 to 365 F.,22.5 mol percent naphthenes. Catalyst: 0.6 percent by weight ofplatinum, 0.7 percent by weight of chlorine on eta alumina support.

Reactor 7 1st 2nd 3rd Relative Catalyst Fill Pressure, p.s.i.g NitrogenLevels Naphtha Feed p.p.m. wt Reactor Influent, p.p.m. mol ReactorEfliuent, p.p.m. mol Reaction Conditions LHSV, v./hr./v. (overall). 1.Hydrogen to Naphtha, mol ratio 6/1 Octane Severity, CH- (R+O) 101. 6

Days on stream 10 39 60 Yields:

Cm. Reformate, percent vol. oicharge. 59. 2 H1 production, s.c.i./bbl580 Hz in recycle gas, mol percent 1 62. 5 0 's percent vol. of charge11. 0 C s percent vol. oi charge C1 to C3 percent wt. of charge ACM-Reiormate, percent vol AH; Produced, s.c.f./bb1 AH in recycle gas, molpercent Base Section B Charge Stock: Heavy Kuwait Naphtha, BR: 250 to365 F., 24.6 vol. percent Naphthenes. Catalyst: 0.6 percentby weight ofplatinum, 0.7 percent by weight of chlorine on eta alumina support.

Reactor 1st 2nd 3rd Relative Catalyst Fill" Pressure, p.s.i.g

Nitrogen Levels Naphtha Feed 1 Reactor Influent, p.p.m. mol... ReactorEfiluent, p.p.m. mol--- Reaction Conditions, LHSV, v./hr./ 1. Hydrogento Naphtha, mol ratio 8/ Octane Severity, OH (R+O) 99 Days on stream 410 Yields:

05+ Reiormate, percent vol. of charge 70. H2 Production, s.c.i./bbl

Hz in recycle gas, mol peree 05's percent vol. of charge. 0.,s percentvol. of charge. C1 to C3 percent wt. of charge AC Reiormate, percent volAH: Produced, s.c.i.[bbl AH; in recycle gas, mol percent BaseLHSV-Liquid Hourly Space Velocity. v I Naphtha feed and recycle gasstream dried with molecular sieve having pores 4-5 Angstroms indiameter. 2 Pyridine added to charge mixture.

Upon examining the data presented in Table VI, Section A, it will befound that after thirty-nine days on In more detail for the operationwithout nitrogen stream at desiccated reforming conditions withoutaddition, a 180-365 F. paraffinic heavy naphtha was nitrogen addition 1)the yield of C reformate dereformed over a platinum catalyst distributedin a O.5:1:1 creased 1.8 percent (2) the yield of hydrogen per barrelfill ratio in a three-adiabatic reactor system at a liquid decreased 100s.c.f. and (3) the hydrogen content of the hourly space velocity of 1.0v./hr./v., 6/1 hydrogen to recycle gas dropped 4.8 mol percent.Furthermore, the naphtha mol ratio and 101.6 (R-l-O)C reformate octane.

selectivity of the catalyst continued to drop off with onnumberseverity. The naphtha feed and recycle gas streams stream time evidencedby the yields shown in Section A were dried with 4A molecular sieves togive comparable for 60, 80, and 105 days on stream. conditions ofdryness to those used for the desiccated" On the other hand, with asimilar paraffinic naphtha reforming system previously described hereinfor the feed and approximately the same reforming conditions lowpressure reforming studies of the effect of nitrogen except thatnitrogen as pyridine was added to the feed on catalyst selectivity. Inthe high pressure study without the data presented in Table VI, SectionB, show that 5 nitrogen a 0 reformate with an octane rating of afterthirty-nine days on stream (1) the yield of C 101.6 (R+O) was maintainedfor 105 days at which reformate increased 1.3 percent (2) the yield ofhydrogen point the run was concluded having reached an arbitrarily perbarrel increased 80 s.c.f. and (3) the hydrogen set vapor inlettemperature of 980 F. As mentioned content of the recycle gas wasessentially unchanged. earlier, based on the data presented in Table VI,section Thus, from the data presented in Table VI it is manifest A, theselectivity of the catalyst in this system decreased that the admixtureof certain nitrogen-containing comsteadily with on-stream timethroughout the entire run. pounds to the feed (in this case, 5 to 20ppm. wt. Desiccated reforming conditions as in the case of the nitrogenbased on naphtha) when reforming a parafiinic low pressure reformingwere chosen since the on-stream heavy naphtha at high pressurestabilizes the selectivity time is substantially increased overconditions where a of the platinum-group metal reforming catalysts. 7wet system (naphtha feed dried only) is used.

ions, the nitrogen connitrogen level. Under these condit nly naphthadried with molecular sieve material having pores 4 to 5 Angstroms indiameter. Pyridine added to charge mixture.

The study the following table.

with nitrogen added to the 250-365 F. iparaffinic heav the boiling rangeof that which was used in the composition of this stock 17 Thedatavobtained when only the naphtha was dried and no ammonia was admixedwith the charge mixture provided a moisture level of the order of apartial pressure of water of 2.0 mm. Hg in the eifiuent of the tail 18stream at total reaction zone pressure less than 700 p.s.i.g. andpreferably inthe range of 100 to 600 p.s.i.g. and especially in therange of about 200 to 500 p.s.i.g. The vapor inlet temperature(s) is inthe range of 900 reactor. It will be observed that in the absence ofamto 1050 F. dependent upon the activity of the reforming monia infifty-six days on stream, the yield of C reforcatalyst in the presenceof said nitrogen-containing commate decreased'3.2 percent. During thesame on-stream' pound, the liquid. hourly space velocity, and the octaneperiod while the amount of hydrogen produced was subrating (Research-l-3cc. TEL) of the stabilized reformate. stantially constant, neverthelessthe purity of the hydro- Those skilled in'the art will also recognizethat the gen decreased about 3.7 mol percent. present invention providesfor stabilizing the selectivity When a somewhat similar paraflinic stockalso was reof platinum group metal reforming catalyst at pressuresformed at 500 p.s.i.g. but ammonia (as pyridine) was in excess of 400p.s.i.g. and at partial pressures of water added to the charge mixturethe yield of C reformate vapors of the reforming zone in excess of 0.4mm. of increased 1.6 percent in the first seventeen days on streammercury and as high as 2 to 5 to 20 mm. of mercury in and the increasedyield was maintained for the following which the moisture content of atleast one of the charge twenty-eight days. The production of hydrogenincreased naphtha, the hydrogen-containing recycle. gas, and the duringthe first ten days on stream and the increased platinum group reformingcatalyst is regulated to mainproduction of hydrogen was maintainedduring the rest tain the partial pressure of water vapor in reformingzone of the on-stream period, i.e., for thirty-five days. Furtherinexcess of 0.4 mm. of mercury and in the range of 2 more, the purity ofthe recycle hydrogen increased to to 20 and particularly 2 to 5 mm. ofmercury. The seleca maximum at the seventeenth day on stream. While thetivity of the platinum group metal reforming catalyst on purity thendecreased at the end of the forty-five days a refractory oxide supportand acid sites is stabilized by on stream, the purity of the recyclehydrogen was still admixing with the influent of the reforming zone atleast 2.4 mol percent higher than the base when no ammonia one andpreferably atleast 10 and especially 10 to 15 was mixed with thereaction vapors. p.p.m. of ammonia by weight based on charge naphtha.

Illustrative of the characteristics of Mid-Eastem naph- When ammonia isadmixed with the influent of the thas are the following data: reformingzone as described hereinbefore, the selectivity Boiling Range ofFraction IBP190 F, IBP-190 F. 190365 F. 365 F.+

Percent Volume of Full Boiling 100 18. 4 65. 5 16. 1 Range NaphthaDistillation, ASTM" IBP 104 so 182 369 10% voL. 160 94 219 386 50% vol276 108 269 394 90% vol. 366 13s 336 409 EBP 408 165 364 440 OctaneNumber:

Research, clear 39. 8 74. 7 36. 0 9.0

Research+3 cc. TEL 66. 6 91. 5 66. 0 39. 0 06+ Components:

Parafiinsmol percent 87.8 64.3 54.2

Mono olefins, mol percent N aphthenes 2. 8 22. 5 23. 5

Aromatics 9. 4 13. 2 22.3

Thus it is manifest that the addition of nitrogen compounds, which underreforming conditions of temperature, of the platinum group metalreforming catalyst of the pressure, and liquid hourly space velocity inthe presence class described hereinbefore is stabilized when reformingof platinum-group metal reforming catalyst and hydrogen is carried outin excess of 400 p.s.i.g., the temperature yield ammonia, to theinfluent of a reforming zone, i.e., in the range of 900 to 1050 F.depending upon the acthe influent of the first reactor of a multireactorreforming tivity of the reforming catalyst in the presence of the unitstabilizes the platinum-group metal reforming catalyst admixednitrogen-containing compound at a hydrogen when the partial pressure ofwater in the tail reactor efmol ratio in the range of 3 to 15 and aliquid hourly fluent or reforming zone eflluent is as high as 2 to 5 tospace velocity depending upon the activity of the reform 20 mm. Hg at500 p.s.i.g. ing catalyst and the predetermined octane rating of theFrom the foregoing description of the present invenstabilizedreformate.tion those skilled in the art will recognize that the What is claimedis: present invention provides a means of stabilizing the se- The methodof stabilizing the selectivity of platinumlectivity of platinum-groupmetal reforming catalyst group metal reforming which comprises for atleast which comprises regulating the moisture content of at dayscontacting conditioned platinum-group metal reformleast one of chargenaphtha, the hydrogen-containing 0 ing catalyst comprisingplatinum-group metal on refracrecycle gas, and the platinum-group metalreforming tory oxide support having acid sites with charge naphthacatalyst to maintain a partial pressure of watervapor in containinginnocuous concentrations of not more than the final effiuent of thereaction zone, i.e., the efiiuent 20 p.p.m. of sulfur, not more than 1p.p.m. nitrogen and of the tail reactor of a reaction zone having aplurality not more than 1/10 parts of arsenic at least fifteen perofreactors, less than 0.4 and preferably in the range 5 cent by volume ofnaphthenes in the presence of hydrogenof 0.05 to 0.2 millimeter ofmercury and admixing with containing gas in a reforming zone comprisinga plurality the influent vapors of said reaction zone, i.e., theinfluent of reactors, at a pressure in excess of 400 p.s.i.g., mainofthe head reactor of a reaction zone having a plurality taining a partialpressure of water in excess of 0.4 mm. of reactors a nitrogen-containingcompound yielding am- Hg but not greater than about 20 mm. of Hg asmeasmonia in the presence of said platinum-group metal re- 7 ured in theetliuent of the tail reactor, admixing at least forming catalyst andhydrogen, preferably without also one nitrogen compound yielding ammoniaunder said yielding water, in amount sufiicient to supply at least 2reforming conditions at the rate of at least 2 p.p.m. by and preferablyat least 10 p.p.m. of ammonia by weight weight of ammonia based upon thecharge naphtha, said based on the charge naphtha. In a unit having apluhydrogen-containing gas being present in the ratio of rality ofreactors all of the reactors normally being on 7 about three to abouttwenty mols of hydrogen per mol of charge naphtha, employing a reformingtemperature in 952,611 9/1960 Haxton etal. Q. 208-65 the range of about900 to about 1,050 F. and a liquid 2,955,080 10/1960 Carter 208-141hourly space velocity in the range of 0.5 to 2. 2,971,902 2/ 1961 Blom'eet a1. 208141 References Cited i 5 DELBERT E; GANTZ, Prim'ary Examigzen.UNITED STATES PATENTS ALPHONSO D. SULLIVAN, Examiner. 2,872,492 2/1959-Dona1dson et a1. 1---- 208-141 H LEVINE Assistant E i 2,906,699 9/1959Haense1 et a1. 208141 UNITED STATES PATENT OFFICE CERTIFICATE OFCORRECTION Patent No. 3,347,782 October 17, 1967 Leon M. Capsuto et a1.

It is hereby certified that error appears in the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below.

Column 3, line 7, after "having a sup-" insert port comprisingrefractory oxide having acid sites is columns 3 and 4, TABLE II, seventhcolumn, line 2 thereof, for "707" read 77D TABLE III, in the heading,for "C read C column 6, line 52, for "0.5 2" read 0.5 to 2 column 8,line 36, for "exces" read excess column 12, line 27, for "selectively"read selectivity columns 13 and 14, TABLE VI section A, column 60, line2 thereof, for "534" read 435 Signed and sealed this 19th day ofNovember 1968.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. EDWARD J. BRENNER Attesting Officer Commissionerof Patents

